Maybe problem [here](https://github.com/geany/geany-plugins/blob/master/geanylua/glspi_dlg.c#L14): `GTK_MESSAGE_OTHER` (without icon) replaced by `GTK_MESSAGE_INFO` (with icon)?
Well, IIUC that just aliases `GTK_MESSAGE_OTHER` to `GTK_MESSAGE_INFO` on GTK < 2.10 (presumably because `GTK_MESSAGE_OTHER` is new in 2.10 or something like that?). Should not affect GTK 2.24 vs 3.x AFAICT.